Jigs including a contact portion that contacts a molten resin desirably have a good property of releasing a resin from the contact portion. For example, for a jig including a contact portion that contacts a molten resin that flows, such as an extrusion molding mold, an improvement in a releasing property is desired for the purpose of, for example, preventing the generation of “die lip build-up (also referred to as burr or die drool)”, which may cause defects in products, decreasing the feeding/extrusion pressure (improvement in slipperiness), maintaining practical durability of the jig, and improving the appearance of products. This point will now be described using an extrusion molding mold as an example.
In general, long resin molded articles such as wire coatings, wire tubes, and special products whose cross sections are special shapes are formed by extrusion molding. Extrusion molding is conducted by extruding a resin in a molten state from an extrusion molding mold with an extruder. FIG. 4 is a cross-sectional view that schematically shows an example of an extrusion molding mold used for molding a hollow product. In FIG. 4, reference numeral 1 denotes an extrusion molding mold, reference numeral 11 denotes a die, and reference numeral 12 denotes a point. A resin in a molten state is extruded in the direction shown by the arrow in the figure, and is solidified by air cooling or accelerated cooling. Thus, for example, a tube-shaped resin molded article P is produced. The cross-sectional shape of the resin molded article is substantially determined by the shapes of the extrusion molding mold, the die 11, the point 12, etc.
In conducting extrusion molding, a roughened appearance may be generated because some materials have poor slipperiness. Burrs B may also be generated on edges of the extrusion molding mold. In the case where molding is conducted by using such materials, additives for improving the slipperiness are used. However, in the cases where thermoplastic elastomers such as polyester elastomers or plastics containing rubber components are molded, even when additives are used, the generation of the burrs B on the edges of the extrusion molding mold cannot be sufficiently prevented.
Examples of known methods for suppressing the generation of such a roughened appearance and the generation of burrs B include providing a coating composed of polytetrafluoroethylene (PTFE), which has a good releasing property, and the use of an extrusion molding mold in which PTFE is embedded in a tip thereof (for example, PTL 1 and PTL 2).